This invention relates to navigation light sources provided for aircraft that are used to render the aircraft visible, and more particularly to navigation lights for military aircraft that may wish to exercise an option of going to a covert mode of operation in which the only light generated by the aircraft is infra red (xe2x80x9cIRxe2x80x9d) light that can only be seen by friendly military wearing appropriate night vision goggles. The invention also relates to methods of upgrading the covert capabilities of existing aircraft that do not yet have covert IR navigational lights.
The Federal Aviation Administration and the aviation authorities of many countries require that aircraft have navigational lighting generally red lights on the left side and green lights on the right side of the plane, to improve their visibility at night.
Military aircraft, when in civilian airspace on non-covert activities, are also required to have such lighting. Normally, the external lighting is provided by incandescent light bulbs in sockets on the outside of the plane. These are conventionally powered by electricity from the internal electronics of the aircraft, which in most U.S. fighter aircraft is 400 Hz AC at 115 volts. A single double wire runs to each light bulb. The pilot can adjust the intensity of the navigation lights or turn them off completely with a brightness control dial in the cockpit which varies the voltage of the AC current sent to the light socket. In situations where visibility would be a disadvantage, these military aircraft would in the past simply turn off the external lighting.
In recent years, it was noted that in covert activities the aircraft was not visible to the enemy, but also not visible to friendly aircraft, and planes began to be supplied with covert mode IR light sources in addition to the visible navigational lights. The IR light emitted is not visible to the human eye, but can be seen with appropriate viewing equipment, e.g., night vision goggles.
To upgrade aircraft to covert IR capability, IR light sources of this type have ordinarily been additional arrays of IR diodes added to the outside of the plane in addition to the existing navigational lights. Alternatively, filters have been mounted over the existing navigational lights and IR diodes mounted in the light bulb fixtures. These kinds of additions, however, require substantial structural work to create the mounts and to wire the new fixtures into the aircraft body, which usually does not have very much extra room for more wiring. In addition, the extensive modifications result in considerable expense for an upgrade to covert IR capability.
It is accordingly an object of the invention to provide an aircraft lighting system that can function both as a visible navigational light system and also as a covert IR light system for friendly eyes only. It is also an object of the invention to provide a design and method that allows for relatively easy upgrade of existing visible navigation lights to give an existing aircraft IR covert capability without the need for any substantial mechanical adaptation of the plane""s structure.
These and other objectives are accomplished by providing according to the invention a dual mode light source unit configured so that it can be secured into a conventional incandescent bulb socket on the aircraft. The light source has a connector portion that fits in the socket and receives the electrical current supplied thereto by the aircraft electrical system. The unit also comprises electric circuitry connected with the connector portion and a visible light source and an IR light source.
The electric circuitry is configured to process the input current from the socket and based thereon, operate in either a civilian visible mode or a covert IR mode. Where the current is in one electrical state, such as for example a certain voltage, the electric circuit sends power to the visible light source. When the current is in a different electrical state, e.g., a different voltage level, the circuitry sends power only to the IR source and no visible light is emitted. The electrical states of the current may be any variation of electrical parameters thereof, including amperage, voltage, frequency, or data encoded therein, etc.
Such a system allows for ready upgrade of existing aircraft because all control may be accomplished over a single pair of wires, as are already in existing systems that do not have IR mode capability. To upgrade, light source units according to the invention are simply inserted into the existing navigational light sockets.
Other objects and advantages of the invention will become apparent from the specification herein.